FIELD OF THE INVENTION
The invention relates to a configuration for contactless detection of the rpm or speed or of the position of a sensor part of ferromagnetic material being rotatable about an axis or linearly movable and having teeth or at least one segment, including a differential Hall sensor having a carrier plate with two sides, a permanent magnet disposed on one of the sides, and Hall elements secured on the other of the sides for scanning teeth or segments and gaps of the sensor part.
Such a configuration is known from a Siemens publication entitled Differential Gear Tooth Sensor IC TLE 4920 F/G.
The known differential Hall sensor includes two Hall elements which are secured to one side of a carrier plate that has another side on which a permanent magnet is disposed. The magnetic flux of the magnet penetrates both Hall elements simultaneously with the same flux density. If a soft magnetic part is moved past the Hall elements, then the two Hall elements are affected, depending on the position of the part. The influence can be detected from the output signal of an evaluation circuit connected to the Hall elements. For both the static and the dynamic case (relative standstill or relative motion between the Hall sensor and the sensor part), the same output signal results. If the width of the segments in motion is greater than the distance between the two Hall elements, then although the transition between the segment and a gap, or a gap and a segment, can be detected, nevertheless it cannot be detected whether the differential Hall sensor is located precisely above a segment or above a gap.